The present invention relates to a low-temperature firing ceramic composition, a process for producing the composition, and a wiring substrate prepared by using the composition.
Hitherto, alumina has been widely used as an inorganic insulating material used for multilayer circuit substrates, semiconductor packages and the like. In view of recent years trends toward higher processing speed, higher frequency for use, higher wiring density and the like, there is a demand for another inorganic insulating material (i.e., an alternative to alumina) that can be co-fired together with a low-melting-point material (e.g., Au, Ag or Cu), which is low in dielectric constant and resistivity, in place of a high-melting-point material (e.g., W or Mo), and that has a small specific dielectric constant in a high frequency region and a small dielectric loss. As such inorganic insulating materials, there are glass ceramic composites prepared by mixing an amorphous powder(s) with a crystalline powder(s). Such amorphous powders are used for improving sinterability at low temperatures.
Japanese Patent Laid-open Publication JP-A-11-106252 discloses a low-temperature firing glass-ceramic material prepared by adding 0.01-1 wt % of a crystal nucleus powder. U.S. Pat. No. 5,660,781, corresponding to JP-A-8-73233, discloses a process for preparing boron-containing glass ceramic green sheets. JP-A-4-321293 discloses a composition for circuit board, containing an inorganic filler and a special glass frit. JP-A-6-338686 discloses a process for producing a multilayer substrate that is a laminate of glass-ceramic insulating layers and inner wiring patterns. JP-A-7-111372 discloses a low-temperature firing ceramic composition containing 50-70 wt % of a special glass powder and 30-50 wt % of Al2O3 powder. JP-A-6-333429 discloses a high-frequency dielectric ceramic composition. JP-A-7-58454 discloses a glass-ceramic multilayer substrate having a composition of 40-80 wt % of a special glass component and 20-60 wt % of a filler component.
It is an object of the present invention to provide a low-temperature firing ceramic composition which enables a co-firing together with a low-boiling-point material and an effective degreasing and has a low dielectric constant, a low dielectric loss and a high thermal expansion.
It is another object of the present invention to provide a process for stably producing such low-temperature firing ceramic composition.
It is still another object of the present invention to provide a wiring substrate prepared by using such low-temperature firing composition, which is substantially free of warp and wave.
According to the present invention, there is provided a low-temperature firing ceramic composition, comprising Sr2MgSi2O7 crystals forming a major crystal phase of said composition.
According to the present invention, there is provided a first process for producing a low-temperature firing ceramic composition, comprising:
(a) providing a calcination product comprising a major component of at least one of Sr2MgSi2O7 crystal, SrSiO3 crystal and MgSiO3 crystal;
(b) providing a powder mixture comprising 70-99.7 wt % of said calcination product, 0.1-10 wt % of Al, 0.1-10 wt % of B and 0.1-10 wt % of an alkali metal, based on a total weight of said calcination product, said Al, said B and said alkali metal, in terms of oxides in case of said Al, said B and said alkali metal;
(c) shaping said powder mixture into a green body; and
(d) firing said green body at a temperature of 850-1,000xc2x0 C.
According to the present invention, there is provided a second process for producing a low-temperature firing ceramic composition, comprising:
(a) providing a calcination product comprising a major component of at least one of Sr2MgSi2O7 crystal, SrSiO3 crystal and MgSiO3 crystal;
(b) providing a powder mixture comprising 65-99.6 wt % of said calcination product, 0.1-10 wt % of Al, 0.1-10 wt % of B, 0.1-10 wt % of an alkali metal and 0.1-5 wt % of a transition metal that is at least one selected from the group consisting of Mn, Ce, Cr, Cu, Co and Ni, based on a total weight of said calcination product, said Al, said B, said alkali metal and said transition metal, in terms of oxides in case of said Al, said B, said alkali metal and said transition metal;
(c) shaping said powder mixture into a green body; and
(d) firing said green body at a temperature of 850-1,000xc2x0 C.
According to the present invention, there is provided a wiring substrate comprising:
a laminate of green sheets each comprising a low-temperature firing ceramic composition comprising Sr2MgSi2O7 crystals forming a major crystal phase of said composition; and
a wiring pattern formed in an inside of said laminate and/or on a surface of said laminate.